/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.io.support;

import java.util.Locale;

import org.springframework.core.io.DefaultResourceLoader;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Helper class for loading a localized resource,
 * specified through name, extension and current locale.
 *
 * @author Juergen Hoeller
 * @since 1.2.5
 */
public class LocalizedResourceHelper {

    /**
     * The default separator to use inbetween file name parts: an underscore
     */
    public static final String DEFAULT_SEPARATOR = "_";


    private final ResourceLoader resourceLoader;

    private String separator = DEFAULT_SEPARATOR;


    /**
     * Create a new LocalizedResourceHelper with a DefaultResourceLoader.
     *
     * @see org.springframework.core.io.DefaultResourceLoader
     */
    public LocalizedResourceHelper() {
        this.resourceLoader = new DefaultResourceLoader();
    }

    /**
     * Create a new LocalizedResourceHelper with the given ResourceLoader.
     *
     * @param resourceLoader the ResourceLoader to use
     */
    public LocalizedResourceHelper(ResourceLoader resourceLoader) {
        Assert.notNull(resourceLoader, "ResourceLoader must not be null");
        this.resourceLoader = resourceLoader;
    }

    /**
     * Set the separator to use inbetween file name parts.
     * Default is an underscore ("_").
     */
    public void setSeparator(@Nullable String separator) {
        this.separator = (separator != null ? separator : DEFAULT_SEPARATOR);
    }


    /**
     * Find the most specific localized resource for the given name,
     * extension and locale:
     * <p>The file will be searched with locations in the following order,
     * similar to {@code java.util.ResourceBundle}'s search order:
     * <ul>
     * <li>[name]_[language]_[country]_[variant][extension]
     * <li>[name]_[language]_[country][extension]
     * <li>[name]_[language][extension]
     * <li>[name][extension]
     * </ul>
     * <p>If none of the specific files can be found, a resource
     * descriptor for the default location will be returned.
     *
     * @param name      the name of the file, without localization part nor extension
     * @param extension the file extension (e.g. ".xls")
     * @param locale    the current locale (may be {@code null})
     * @return the most specific localized resource found
     * @see java.util.ResourceBundle
     */
    public Resource findLocalizedResource(String name, String extension, @Nullable Locale locale) {
        Assert.notNull(name, "Name must not be null");
        Assert.notNull(extension, "Extension must not be null");

        Resource resource = null;

        if (locale != null) {
            String lang = locale.getLanguage();
            String country = locale.getCountry();
            String variant = locale.getVariant();

            // Check for file with language, country and variant localization.
            if (variant.length() > 0) {
                String location =
                        name + this.separator + lang + this.separator + country + this.separator + variant + extension;
                resource = this.resourceLoader.getResource(location);
            }

            // Check for file with language and country localization.
            if ((resource == null || !resource.exists()) && country.length() > 0) {
                String location = name + this.separator + lang + this.separator + country + extension;
                resource = this.resourceLoader.getResource(location);
            }

            // Check for document with language localization.
            if ((resource == null || !resource.exists()) && lang.length() > 0) {
                String location = name + this.separator + lang + extension;
                resource = this.resourceLoader.getResource(location);
            }
        }

        // Check for document without localization.
        if (resource == null || !resource.exists()) {
            String location = name + extension;
            resource = this.resourceLoader.getResource(location);
        }

        return resource;
    }

}
